Multiplexing system for selection of notes in an electronic musical instrument

ABSTRACT

In an electronic musical instrument, such as an organ, the instrument includes a keyboard with playing keys corresponding to the notes of musical scale to be sounded plus other keys or stops which are actuated to cause other musical sounds to be produced which are related in frequency in accordance with certain predetermined relationships to notes produced by actuation of the playing keys. The playing keys and stop keys are operatively coupled into a switch matrix for closing of switches therein, such switch closures being sequentially scanned for converting the parallel switch closure data into serial time division multiplexed data. The stop data is stored and used to control circuitry responsive to the playing key data for inserting into the serial data stream additional data bits corresponding to additional notes to be coupled to those notes associated with playing keys actually played. The combined serial data is then fed to a serial-to-parallel converter the output of which is fed to a bank of tone generators for sounding the notes of the musical scale. Alternating reiteration (marimba beat) is obtained by actuation of one of the stop keys which produces a signal operative upon the serial stream of note data to repetitively and alternately eliminate, at a subaudible frequency, from the note bit stream those notes falling within first one group and then within a second group of notes in each octave of the musical scale, thereby producing a marimba beat.

United States Patent [191 Kmetz 1 Apr. 8, 1975 Gerald L. Kmetz. San Jose. Calif.

[73] Assignee: National Semiconductor Corporation, Santa Clara. Calif.

22 Filed: Aug. 23, 1974 [211 App]. No.: 500,138

[75] lnventor:

[52] U.S. Cl ..84/l.0l;84/1.24 [51] Int. Cl. Gl0h 1/02; GlOh 5/00 [58] Field of Search 84/10], 1.03, 1.24, 1.25

[56] References Cited UNITED STATES PATENTS 3.511792 6/1970 Deutsch 84/].03 3 594 487 7/1971 Jones, Jr. 84/l.0l UX 3,610,799 10/1971 Watson 84/].01

3.610800 10/1971 Deutsch 84/101 3,697,661 10/1972 Deutsch..... 84/].01 3,740.450 6/1973 Deutsch 84/124 3.746.773 7/1973 Vetrecht 84/l.0l 3.757.022 9/1973 Markowitz..... 84/125 3.794.748 2/1974 Deutsch 84/124 3 809 786 5/1974 Deutsch..... 84/1111 5/1974 Deutsch 84/124 Primary Evaluator-Stephen J. Tomsky Assistant E.\'uminw'Stanley J. Witkowski [57] ABSTRACT In an electronic musical instrument, such as an organ, the instrument includes a keyboard with playing keys corresponding to the notes of musical scale to be sounded plus other keys or stops which are actuated to cause other musical sounds to be produced which are related in frequency in accordance with certain predetermined relationships to notes produced by actuation of the playing keys. The playing keys and stop keys are operatively coupled into a switch matrix for closing of switches therein, such switch closures being sequentially scanned for converting the parallel switch closure data into serial time division multiplexed data. The stop data is stored and used to control circuitry responsive to the playing key data for inserting into the serial data stream additional data bits corresponding to additional notes to be coupled to those notes associated with playing keys actually played. The combined serial data is then fedv to a serial-to-parallel converter the output of which is fed to a bank of tone generators for sounding the notes of the musical scale. Alternating reiteration (marimba beat) is obtained by actuation of one of the stop keys which produces a signal operative upon the serial stream of note data to repetitively and alternately eliminate, at a subaudible frequency, from the note bit stream those notes falling within first one group and then within a second group of notes in each octave of the musical scale, thereby producing a marimba beat.

8 Claims, 5 Drawing Figures 48 BIT DELAY SHIFT REGISTER PATENTEU 1: 3,875,842

SHEET 1 0F 2 sTATE I44 I NOTE J ocTAvE Z CLOCK COUNTER COUNTER STATE m I00 KHz (l2 BIT RING (l2 BIT RING 5 ATE 23 COUNTER) COUNTER) J 0 CF I F/F 7 2T0 STOPS 23 L/ MULT| KEYS 6| PLEXER w 84 TIME SLOTS 28 70 3 sERIAL-To- I 29 PARALLEL F/g'5 M l V CONVERTER STRAIGHT I 34 IIIIIIIIIIII 6 5 6/ Y I Q Q) SUB. OCT.35 36 I 2 L. L. X [SUPER ocTAvE 44 I Z I UN|$QN 7 DELAY Q) 72 l 2 I \I8' (UNISON) 3/ 32 We) 76 l 24 BIT DELAY I SHIFT fif I J REGISTER l 4- K64 2 0 I F /g i (B+D) I 58 l5 l6 I9 24 3| 36 4O 43 48 BIT DELAY SHIFT REGISTER UNIFIED 22) 2;) V

SEEKET 2 OF 2 ,2; 85 BIT S/P CONVERTER 45 STRAIGHT voIcE TONE GENERATOR /0 UNIFIEDVOICE TONE GENERATOR YI' 2g 97 BIT SIP CONVERTER V9 Fig-2 CP 0 I INE /4 86 VARIABLE Q FREQ. T F: -35 LOW FREQ. i

osc 2f Q 82 II II '-eEI\IERAToR l 83 LOGIC "Hf Lg V V T REIT ON WV Hg. 4' MULTIPLEXER IQ (u)2 f IIIIIII|| (b) I, I

(c) I REIT 4/OFF (d) 02 I I I I TIME MULTIPLEXING SYSTEM FOR SELECTION OF NOTES IN AN ELECTRONIC MUSICAL INSTRUMENT BACKGROUND OF THE INVENTION The present invention relates in general to electronic musical instruments and more particularly to such instruments of the type wherein keyboard data is converted from parallel to serial time division multiplexed data which is modified in certain ways to produce certain desired musical notes. The modified serial stream is converted into parallel format and thence fed to an array of tone generators for sounding the notes.

DESCRIPTION OF THE PRIOR ART Heretofore, an electronic organ has been proposed of the type wherein a principal keyboard, with key switches corresponding to notes on the musical scale, is sequentially scanned to convert parallel keyboard switch closure data, corresponding to striking of certain keys, into a serial time division multiplexed data stream. This stream of data is thence fed to a second circuit, namely, a delay shift register wherein certain delayed bit outputs are added to the data stream in accordance with switch closures associated with closure of certain stop keys (another keyboard) so that the output corresponding to closure of the stop keys, namely coupled notes, are added to the serial stream generated by closure of playing keys in the first keyboard. The composite data stream is thence fed in serial format to a serial-to-parallel converter which converts the serial data into parallel outputs for actuation of a bank of tone generators. Such a musical instrument is disclosed in U.S. Pat. No. 3,697,661 issued Oct. 10, 1972.

It has also been proposed, in an electronic musical instrument, such as an organ, to employ a switching array wherein the switches of the array are actuated by playing of keys in a keyboard. Key actuated switch closures are repetitively and sequentially scanned to produce a time division multiplexed signal which is thence fed to a generator assignment logic circuit for generating signals representative of certain desired tones in the musical scale associated with respective ones of the switch closures. These outputs of the tone generators I are utilized for sounding the audio tones or notes of the musical scale.

Stop keys were also provided. These keys were separately scanned to produce a time division multiplexed signal which was thence decoded for calling up of certain desired tones from a tone memory bank. Such a musical instrument is disclosed in U.S. Pat. No. 3,610,799 issued Oct. 5, 1971.

SUMMARY OF THE PRESENT INVENTION The principal object of the present invention is the provision of an improved multiplexing system for selection of notes in an electronic musical instrument.

In one feature of the present invention, switch closures corresponding to playing keys of the musical scale are scanned to produce a first time division multiplexed signal component. Switch closures corresponding to the selection of stop keys or coupler keys are also scanned to produce a second time division multiplexed signal component. This latter component is stored and the stored signals are employed for operation on the playing key signal component to derive a composite time division multiplexed output which is thence converted to parallel format for energization of respective tone generators.

In another feature of the present invention, switch closures corresponding to actuation of playing keys of the keyboard of the musical instrument are repetitively and sequentially scanned to produce a time division multiplexed signal. A circuit is actuated in response to depression of another key for dividing the notes of the musical scale in each octave into a certain predetermined number of groups and for alternately disabling response to notes which have been played in first one of these groups and then the other one of these groups at a subaudible rate for generation of a marimba type of heat.

Other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic circuit diagram, partly in block diagram form, of a portion of the circuitry of the electronic organ of the present invention,

FIG. 2 is a schematic circuit diagram, similar to that of FIG. 1, depicting the remaining portion of the circuitry of the electronic organ of the present invention,

FIG. 3 is a schematic circuit diagram of one of the switches in the switch matrix of FIG. 1, and

FIG. 4 is a schematic circuit diagram of a portion of the circuit of FIG. 1.

FIG. 5 shows waveforms associated with the apparatus in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 1 and 2, there is shown the electrical circuitry for an electrical organ incorporating features of the present invention. The organ includes a switch matrix 11 having twelve columns and seven rows to constitute a total matrix of 84 switches, each switch being actuated by a key of a keyboard. The individual switches of the matrix are indicated in FIG. 3 and comprises a switch 12 connected in series with a diode 13 between the horizontal and vertical wires 14 and 15, respectively, of the switch matrix 11, such switch 12, and diode 13 being provided at each intersection of the wires 14 and 15. In a particular arrangement, the stop keys or switches comprise up to 23 switches, whereas the playing keys occupy 61 of the switches. The switch array 11 is scanned from the stop keys through the playing keys, such playing keys being scanned in time from the low frequency to the high frequency end of the musical scale.

The 12 column outputs from the switch matrix 11 are fed to the input of a 12 to l multiplexer 16, such as is exemplified by AND gates 47 through 57 in conjunction with OR gate 59. The rows of the switches namely, the horizontal busses 14, are sequentially energized from the beginning of the stop keys through the high frequency end of the playing keys via 7 outputs derived from the output of an octave counter 17. More particularly, the octave counter 17 has 7 output lines one line connected to each of the respective 7 horizontal busses 14 of the switch matrix 11. As the count in the octave counter advances from a first octave to a second and so forth, the corresponding one of the 7 output busses of the octave counter 17 is energized for energizing the corresponding horizontal buss 14' of the switch matrix 11.

A clock signal generator 18 serves to produce a train of clock pulses at a suitable high frequency such as 100 KHz. The output of the clock pulse generator 18 is fed to the input of a note counter 19 which has 12 individual note output lines in cable 21. Output cable 21 delivers an output pulse for each note being scanned and thus provides output pulses at the clock frequency. The second output line 22 of the note counter 19 corresponds to every 12th note orcorresponds to a pulse per octave. The octave output pulse of the note counter 19 is fed to the octave counter 17 for advancing the output of the octave counter for each octave of notes being scanned.

The twelve output lines of the cable 21 of the note counter 19 are fed to the input of the multiplexer 16 for repetitively stepping the outputs from the switch matrix 11 through the multiplexer 16. In other words, the individual note count output on line 21 starts with the first column of the switch matrix and with each successive pulse advances the input to the multiplexer to each successive column output of the switch matrix 11. Upon the completion of the 12th note being scanned the output 22 of the note counter 19 repeats the sequence of counts across the column of vertical busses of the switch matrix 11.

The switch matrix 11 is energized by the output of the octave counter 17 and scanned by multiplexer 16 first through the 23 stop keys and then through the 61 playing keys to produce a time division multiplexed sig nal at the output of multiplexer 16 having 84 time slots therein. The first 23 time slots corresponding to the time division multiplexed output of the stop keyboard and the next 61 time slots corresponding to the time division multiplexed status of the playing keyboard, wherein the keys correspond to respective notes of the musical scale. The first 23 stop key time slots correspond to coupler signals and any other instructions desired relative to operation of the organ.

The multiplexer 16 thus serves as a parallel-to-serial converter for converting the parallel keyboard information in the switch matrix into serial data at the output of the multiplexer 16.

The first 23 time slots are fed into a serial-to-parallel converter 25 such as a static shift register. The shift register 25 is under the control ofa stop key control circuit 26. The stop key control circuit 26 receives an input from the octave counter 17 corresponding to count 144 or to the beginning count of the scan of the stops 23. This input is responsive in the stop key control circuit to set the Q output state of the flip-flop 27 to a true condition, i.e., state 1. The stop control circuit 26 holds this state for the number of time slots corresponding to the number of stop keys in the switch matrix 11. In the case there are 23 stop keys, the eleventh note line of cable 21 is ANDED with the second octave line output of octave counter17 in AND gate to produce an input to the flip-flop 27 for changing its output state from true'to false. The true output of the flip-flop 27 is ANDED in AND gate 28 with a clockv pulse output CP derived from the clock 18 to produce an output fed to shift register to cause entry of the first 23 time slot bits into the serial-to-parallel converter 25. The true output of flip-flop 27 is also fed to one input ofa second AND gate 29 for ANDING with the serial data stream output of the multiplexer 16 to gate the first 23 time slots of the output of the multiplexer 16 into the serial-to-parallel converter 25. When the flip-flop 27 shifts to a false" condition, the false" output is inverted by an inverter 31 to produce a true output which is ANDED in an AND gate 32 with the serial data stream at the output of the multiplexer 16 for gating the remaining 61 playing key time slot bits into a 24 bit delay shift register 33. Thus, the stop key outputs are fed into the serial-to-parallel converter 25 and the playing key outputs are directed through the 24 bit delay shift register 33.

Three storage outputs 34, 35 and 36 of the serial-toparallel converter 25 correspond to a suboctave coupler output 34, a unison coupler output 35 and a superoctave output 36. Because the playing keys in the switch matrix 11 have been scanned from the low frequency end to the high frequency end, a suboctave coupler output, corresponding to the frequency of a 16 foot length pipe of a pipe organ, is provided by taking the undelayed output of AND gate 32 and ANDING that with the suboctave stop output 34 in AND gate 37. Similarly, the unison output which would correspond to a frequency of an 8 foot length pipe of a pipe organ, is tapped out of the delay shift register 33 at a 12 bit delay point 38 and ANDED with the unison stop output 35 in AND gate 39 to produce the unison coupled output. Likewise, the superoctave stop output 36 is ANDED in AND gate 41 with the 24 bit delayed output 42 corresponding to a 4 foot length pipe of a pipe organ to produce the superoctave output.

The coupled suboctave, unison and superoctave outputs of gates 37, 39 and 41 are fed to the input of an OR gate 43, the output of which is fed through a 12 bit delay 44, such as that obtained by a 12 bit shift register, to produce an output at terminal Y corresponding to what is known in organ art as a straight output. This straight" output consists of a serial bit stream of time division multiplexed bits which will have the coupler function, if any, superimposed. This coupler function is responsive to the selection of respective stop keys and serves to insert note bits into time slots corresponding to one octave lower or higher than that corresponding to the playing of each playing key. Also, if the unison stop key is not selected, the note bits corresponding to the struck playing keys do not appear in the straight" serial bit stream.

This straight serial bit stream is thence fed to one input of an bit serial-to-parallel converter 45 (see FIG. 2). The serial bit stream enters the serial-toparallel converter 45, such as a dual rank shift register of the type disclosed in U.S. Pat. No. 3,697,661. After the bit stream has been entered into the shift register 45 the data is parallel transferred via a strobe signal Z derived from octave counter 17 into the second rank of memory elements of the dual rank serial-to-parallel converter 45. The data in the second rank of memory elements serves as the inputs to a straight voice tone generator 46 for actuating respective ones of 85 different tone generators for generating audio sounds corresponding to notes of the musical scale.

The electronic organ also has the alternative feature of providing additional coupler functions corresponding to what is known in the art as a unified coupler output. In the unified coupler output, additional notes are derived from played notes such additional notes being both whole and fractional octaves away from the played or. unison note. This unified coupler function is obtained in a manner similar to that of the straight coupler function previously described with regard to serial-to-parallel converter 25 and stop keys corresponding'to outputs 34, 35 and 36.

More particularly, there are, for example, 11 different unified coupler stop keys that may be selected for inserting into the first 23 time slots in the output of multiplexer 16. These stop key inputs are stored in the serial-to-parallel converter 25 in positions indicated at l-ll corresponding to outputs X. These X outputs are utilized as one input respectively to AND gates 47-57. The second inputs to such AND gates correspond to pitch delayed bits derived from a 48 bit delay shift register 58 into which either the straight" coupled output derived from OR gate 43 or the non-coupled unison output derived from delay 38 of shift register 33 is applied. The respectively delayed additional signal outputs derived from the outputs of gates 47-57 are fed to an OR gate 59 to produce the unified output Y, which is thence fed to the input of a 97 bit dual rank serial-to-parallel converter 9 which is thence transferred via strobe signal Z into the second rank memory elements for actuation ofa unified voice tone generator for producing the notes associated with the unified" output Y, in the manner as previously described with regard to tone generator 46.

Either the straight" coupled or the non-coupled unison time division multiplexed signal may be fed to the input of the 48 bit shift register 58. Selection of the particular input to shift register 58 is accomplished by actuating the proper stop key in the switch matrix which causes a "true output to appear at output 61 of the serial-to parallel converter if the straight" coupled input to shift register 58 is desired. This true output is applied to the input of an AND gate 62 for ANDlNG with the straight" coupled output of OR gate 43 to cause the straight" coupled output to be fed through OR gate 63 and thence via line 64 to the input of the 48 bit delay shift register 58. If any one or more of the unified coupler stop keys is depressed a corresponding output will appear at output X which will then open the corresponding delay gates 47-57 of shift register 58 and produce the unified" output at the output of OR gate 59. When the output of the serial-to-parallel converter 25 on line 61 is false" or low this will cause the unison output from delay 38 to be fed to the input of the delay shift register 58 via line 64. More particularly, the output of 61 is fed to the input of a second AND gate 65 via an inverter 66 and the second input to the AND gate 65 comprises the unison output from 38 so that a false output at 61 causes the unison output to pass through AND gate 65 and OR gate 63 onto line 64 and thence to the unified shift register 58.

An alternating reiteration enable circuit 70 is connected in series with line 64 for superimposing a marimba beat function on the unified coupled output Y However, when the alternating reiteration circuit is disabled, the signals on line 64 pass through that circuit directly to the shift register 58.

The alternating reiteration or marimba beat producing circuit 70 includes an alternating reiteration enable decoder comprising OR gate 71 which receives individual line inputs from the note counter 19 for subdividing each of the octaves into four three-note groups. For example, group A includes the first three note lines of the octave, group B comprising the next three note lines of the octave, group C the next three, etc. The first and third groups of lines 21 are inputted to the OR gate 71. The output of the OR gate 71 comprises a output and Q52 output at line 72 and 73. The (15, output is true during the interval of time wherein the notes on line 64 will fall within either group A or group C and the output on line 73 is a true whenever the notes on line 64 fall within group B or D. Outputs 72 and 73 are fed to one input of respective AND gates 74 and 75, for ANDlNG with the serial bit stream on line 64 and with stop key outputs 76 and 77 of the serial-to-parallel converter 25 labeled (1), and (1) respectively.

The stop key outputs 76 and 77 are derived in a manner as shown in FIG. 4. More particularly, a variable frequency oscillator 81 operating at a subaudible frequency 2f, of a few Hz has its frequency controlled via the manual setting of a potentiometer 82 for varying a frequency control voltage applied to the oscillator 81 from a source of potential 83 for controlling the frequency 2f of a square wave pulse output voltage, shown as waveform (a). See FIG. 5. A key operated reiteration switch 84, which is independent of the switch matrix 11, controls the output of the oscillator 81. The output of the variable frequency osc illator 81 is fed to a flip-flop 85 having outputs Q and Q at a frequency of f and having waveform (b). The Q output is NANDED in NAND gate 86 with a sample of the waveform (a) and further NANDED in NAND gate 87 with the output of reiteration switch 84 to produce an output (15,. (b, has a waveform (c) as shown in FIG. 4 and comprises a 25 percent duty factor square wave pulse train of frequency f,. Similarly, the Q output of flip-flop 85 is NANDED in NAND 88 with a sample of waveform '(a) and further NANDED in NAND gate 89 with the output of reiteration switch 84 to derive the 4J output of waveform (d). The d), and (1) outputs are applied to nodes 8 between diodes 13 and reverse connected diodes 7 via load resistors 6. The d), and d outputs are scanned in the switch matrix 11 to derive the stop key time slot allocation for storage in shift register 25. More particularly, when the respective outputs 1), and are high and horizontal buss 14 is low, i.e., not energized, the outputs d), and are shunted via diodes 7 onto buss 14, whereas when horizontal buss 14 is energized (high) (1), and 111 when high are conducted via diodes 13 onto the respectively scanned vertical buss 15.

Thus, the qb and (b outputs 76 and 77 comprise two pulse trains out of phase each having a 25 percent duty factor at a frequency of f Thus when the marimba beat key switch 84 is switched to ON a true output appears on line 76 which is ANDED in AND gate 74 to enable only playing of notes falling within groups A and C, whereas in alternate half cycles of f, (the marimba beat or reiteration frequency) the (b output on line 77 is true which is ANDED in AND gate 75 to enable only playing of notes in groups B and D. The output of AND gate 74 and 75 is fed through OR gate 78 to the shift register 58.

In operation, the (b and (1) outputs are true at a subaudible frequency in alternating sequence to produce alternating reiteration of the sounding of the notes in the two groups A and C or B and D. In addition, the output of reiteration switch 84 is fed to the unified tone generator 10 to change the envelope time constants of the sounding of the notes to correspond to a percussive sound as contrasted with the flute sound. This envelope alteration of the sounding of the tone generators from a flute sound to a percussive sound is conventional.

Additional keyboards 11 are accommodated by use of common circuitry such as clock 18, note counter 19 and octave counter 17 together with their respective keyboards ll, multiplexers 16, etc., except that their respective straight outputs Y etc., and unified outputs Y etc., may be applied to the common serial-v to-parallel converters 45 and 9 via OR gates 91 and 92, respectively.

What is claimed is: 1. In an electronic musical instrument having a set of playing switches selectively actuable to cause the production of sounds corresponding to respective notes of the musical scale and a second set of stop switches selectively actuable to cause other sounds to be produced which are related in frequency in accordance with a certain predetermined relationship to notes associated with actuation of said playing switches, the combination including:

means for repetitively and sequentially scanning said playing and stop switches to detect actuation of any one or more thereof and to develop a repetitive time division multiplex signal containing playing signal components corresponding to time division assignments of notes associated with actuation of said playing switches and a stop signal component corresponding to time division assignments of data associated with actuation of said stop switches;

means for receiving and storing said stop signal components corresponding to multiplex data associated with actuation of respective stop switches;

third signal generating means responsive to said stored stop signal components of said multiplex data and to said playing signal components corresponding to time division assignments of notes associated with activation of said playing switches to develop a third time division multiplex signal containing additional time division assignments of notes in said third time division multiplex signal, such additional note assignment signal components of said third signal corresponding to notes related in frequency in a certain predetermined manner determined by activation of said stop switches to notes associated with activation of respective playing switches; and

fourth signal developing means responsive to said third time division multiplex signal and representative of the selective actuation of respective ones of said playing and stop switches for developing a fourth signal output from which to generate sounds to be produced by the electronic musical instrument.

2. The apparatus of claim 1 wherein, the electrical musical instrument comprises an electronic organ, and wherein said receiving and storing means includes a serial-to-parallel converter means for receiving the time division multiplexed stop signal components and converting same to parallel outputs.

3. The apparatus of claim 2 wherein said serial-toparallel converter means includes a shift register means for receiving the stop signal components.

4. The apparatus of claim 1 wherein the electrical musical instrument comprises an electronic organ, and wherein said third signal generating means includes a delay shift register means to which said playing signal components corresponding to time division assignments of notes associated with actuation of respective playing switches are applied.

5. The apparatus of claim 1 including, tone generating means responsive to said fourth signal output for producing tones representative of notes of the musical scale corresponding to selective actuation of said playing and stop switches.

6. The apparatus of claim 5 wherein the electrical musical instrument comprises an electronic organ, said combination further including keyboard means, and wherein said playing and stop sets of switches are coupled in operative relation with respective keys of said keyboard means.

7. The apparatus of claim 1 including, alternating reiterative means for repetitively and alternately eliminating at aa subaudible frequency from said fourth signal output, signal components corresponding to actuation of said playing switches and falling within first one group and then within a second group of notes in each octave of the musical scale.

8. The apparatus of claim 7 wherein said alternating reiterative means includes, means for identifying first and second groups of time slots in one of said time division multiplexed signals, said group of time slots corresponding to first and second groups of notes in each octave of the musical scale, and means for repetitively and alternately eliminating from the time division multiplexed signal at a subaudible frequency those components corresponding to actuation of said playing switches within one and then the other of said first and second groups of time slots. 

1. In an electronic musical instrument having a set of playing switches selectively actuable to cause the production of sounds corresponding to respective notes of the musical scale and a second set of stop switches selectively actuable to cause other sounds to be produced which are related in frequency in accordance with a certain predetermined relationship to notes associated with actuation of said playing switches, the combination including: means for repetitively and sequentially scanning said playing and stop switches to detect actuation of any one or more thereof and to develop a repetitive time division multiplex signal containing playing signal components corresponding to time division assignments of notes associated with actuation of said playing switches and a stop signal component corresponding to time division assignments of data associated with actuation of said stop switches; means for receiving and storing said stop signal components corresponding to multiplex data associated with actuation of respective stop switches; third signal generating means responsive to said stored stop signal components of said multiplex data and to said playing signal components corresponding to time division assignments of notes associated with activation of said playing switches to develop a third time division multiplex signal containing additional time division assignments of notes in said third time division multiplex signal, such additional note assignment signal components of said third signal corresponding to notes related in frequency in a certain predetermined manner determined by activation of said stop switches to notes associated with activation of respective playing switches; and fourth signal developing means responsive to said third time division multiplex signal and representative of the selective actuation of respective ones of said playing and stop switches for developing a fourth signal output from which to generate sounds to be produced by the electronic musical instrument.
 2. The apparatus of claim 1 wherein, the electrical musical instrument comprises an electronic organ, and wherein said receiving and storing means includes a serial-to-parallel converter means for receiving the time division multiplexed stop signal components and converting same to parallel outputs.
 3. The apparatus of claim 2 wherein said serial-to-parallel converter means includes a shift register means for receiving the stop signal components.
 4. The apparatus of claim 1 wherein the electrical musical instrument comprises an electronic organ, and wherein said third signal generating means includes a delay shift register means to which said playing signal components corresponding to time division assignments of notes associated with actuation of respective playing switches are applied.
 5. The apparatus of claim 1 including, tone generating means responsive to said fourth signal output for producing tones representative of notes of the musical scale corresponding to selective actuation of said playing and stop switches.
 6. The apparatus of claim 5 wherein the electrical musical instrument comprises an electronic organ, said combination further including keyboard means, and wherein said playing and stop sets of switches are coupled in operative relation with respective keys of said keyboard means.
 7. The apparatus of claim 1 including, alternating reiterative means for repetitively and alternately eliminating at aa subaudible frequency from said fourth signal output, signal components corresponding to actuation of said playing switches and falling within first one group and then within a second group of notes in each octave of the musical scale.
 8. The apparatus of claim 7 wherein said alternating reiterative means includes, means for identifying first and second groups of time slots in one of said time division multiplexed signals, said group of time slots corresponding to first and second groups of notes in each octave of the musical scale, and means for repetitively and alternately eliminating from the time division multiplexed signal at a subaudible frequency those components corresponding to actuation of said playing switches within one and then the other of said first and second groups of time slots. 